This invention discloses an improvement to a digital Acoustic Echo Control (AEC) in hands-free telephones. It describes an additional adaptive filter referred to as a residual echo filter, which is placed after the usual echo canceller and it is used to efficiently and accurately estimate a residual echo signal b(i) and a system coupling factor β(i), which can be utilized to establish an efficient control for the AEC system and construct the appropriate filters. The invention also describes a control block means performing a joint operation control of the echo canceller, residual echo suppressor and residual echo filter for achieving more consistent echo cancellation results and enhancing output signal quality.
Legal claims defining the scope of protection, as filed with the USPTO.
1. An echo cancellation system ( 11 ), comprising: a microphone ( 18 ), responsive to a resulting echo signal ( 22 ) from a loudspeaker ( 16 ) that provides an acoustic output in response to a speech signal ( 20 ), for providing an echo signal which is a component of a microphone signal ( 28 ); and a control block means ( 40 ), responsive to the speech signal ( 20 ), to an echo reduced microphone signal ( 34 ) and to a further echo reduced microphone signal ( 52 ), for providing a first control signal ( 46 ) to an echo canceller ( 10 ), a second control signal ( 54 ) to a residual echo suppressor ( 14 ) and a third control signal ( 48 ) to a residual echo filter ( 42 ); wherein said control signals are provided for optimizing cancellation of the echo signal.
2. The echo cancellation system ( 11 ) of claim 1 , wherein the first control signal ( 46 ) is a transfer function signal provided to the echo canceller ( 10 ), said transfer function signal weights the voice signal ( 20 ).
3. The echo cancellation system ( 11 ) of claim 1 , wherein the second control signal ( 54 ) is a further transfer function signal provided to the residual echo suppressor ( 14 ), said further transfer function signal weights an echo reduced microphone signal ( 34 ).
4. The echo cancellation system ( 11 ) of claim 1 , wherein the third control signal ( 48 ) is a residual transfer function signal provided to the residual echo filter ( 42 ), said residual transfer function signal weights the voice signal ( 20 ).
5. The echo cancellation system ( 11 ) of claim 1 , further comprising the residual echo filter ( 42 ), responsive to the speech signal ( 20 ) and to the third control signal ( 48 ), for providing a further estimate echo signal ( 50 ) to a further adder ( 44 ).
6. The echo cancellation system ( 11 ) of claim 1 , further comprising the residual echo suppressor ( 14 ), responsive to an echo reduced microphone signal ( 34 ) and to the second control signal ( 54 ), for providing an output system signal ( 36 ).
7. The echo cancellation system ( 11 ) of claim 1 , further comprising the echo canceller ( 10 ), responsive to the voice signal ( 20 ) and to the first control signal ( 42 ), for providing an estimate echo signal ( 32 ) to an adder ( 30 ).
8. The echo cancellation system ( 11 ) of claim 7 , further comprising the residual echo filter ( 42 ), responsive to the speech signal ( 20 ) and to the third control signal ( 48 ), for providing a further estimate echo signal ( 50 ) to a further adder ( 44 ).
9. The echo cancellation system ( 11 ) of claim 8 , further comprising the residual echo suppressor ( 14 ), responsive to the echo reduced microphone signal ( 34 ) and to the second control signal ( 54 ), for providing an output system signal ( 36 ).
10. The echo cancellation system ( 11 ) of claim 1 , further comprising an adder ( 18 ), responsive to a microphone signal ( 28 ) and to an estimate echo signal ( 32 ), for providing an echo reduced microphone signal ( 34 ).
11. The echo cancellation system ( 11 ) of claim 1 , further comprising a further adder ( 44 ), responsive to the echo reduced microphone signal ( 34 ) and to a further estimate echo signal ( 50 ), for providing the further echo reduced microphone signal ( 52 ).
12. The echo cancellation system ( 11 ) of claim 1 , wherein the residual echo filter ( 42 ), the echo canceller ( 10 ) and the residual echo suppressor ( 14 ) operate in a time domain, and said first, second and third control signals ( 46 , 54 , 48 ) are provided in the time domain as well.
13. The echo cancellation system ( 11 ) of claim 1 , wherein the residual echo filter ( 42 ), the echo canceller ( 10 ) and the residual echo suppressor ( 14 ) operate in a frequency domain, and said first and second control signals ( 46 , 54 ) are provided in the frequency domain as well.
14. The echo cancellation system ( 11 ) of claim 1 , wherein the residual echo filter ( 42 ) and the echo canceller ( 10 ) operate in a time domain, and said first and third control signals ( 46 , 48 ) are provided in the time domain as well.
15. The echo cancellation system ( 11 ) of claim 14 , wherein the residual echo suppressor ( 14 ) operates in a frequency domain, and said second control signal ( 54 ) is provided in the frequency domain as well.
16. The echo cancellation system ( 11 ) of claim 14 , wherein the first and the third control signals ( 46 , 48 ) are determined, respectively, as c ( i + 1 ) = c ( i ) + μ 1 ( i ) x ( i ) e ( i ) x ( i ) 2 and h ( i + 1 ) = h ( i ) + μ 2 ( i ) x ( i ) f ( i ) x ( i ) 2 , wherein c(i) is a transfer function signal in the time domain provided to the echo canceller ( 10 ), h(i) is a residual transfer function signal in the time domain provided to the residual echo filter ( 42 ), μ 1 (k) and μ 2 (k) are a step-size signal and a further step-size signal, respectively, x(i) is a voice signal ( 20 ), e(i)=y(i)−c T (i)×(i) is the echo reduced microphone signal ( 34 ), and f(i)=e(i)−h T (i)×(i) is the further echo reduced microphone signal ( 52 ), where y(i) is the microphone signal ( 28 ).
17. The echo cancellation system ( 11 ) of claim 16 , wherein the step-size signal and the further step-size signal, are determined, respectively, as μ 1 ( i ) = β 1 ( i ) x 2 ( i ) _ e 2 ( i ) _ and μ 2 ( i ) = β 2 x 2 ( i ) _ f 2 ( i ) _ , wherein β 2 is a pre-selected constant, {overscore (x 2 (i))} is a voice signal power, {overscore (f 2 (i))} is a further echo reduced microphone signal power, {overscore (e 2 (i))} is an echo reduced microphone signal power, and a coupling factor β 1 (i) is determined as β 1 ( i ) = N L h T ( i ) h ( i ) = N L ∑ k = 0 L - 1 h 2 ( i - k ) , wherein N is an echo canceller ( 10 ) filter length, and L is a residual echo filter ( 42 ) length.
19. The echo cancellation system ( 11 ) of claim 17 , wherein the step-size signal is determined as μ 1 ( i ) = b ′2 ( i ) _ e 2 ( i ) _ wherein {overscore (b′ 2 (i))}=(1−γ)b′ 2 (i)+γ{overscore (b′ 2 (i−1))} is a further estimate echo signal power of a further estimate echo signal b′(i) ( 50 ), wherein 0<γ<1 is a smoothing coefficient and b′(i) ( 50 ) is provided to the control block means ( 40 ).
20. The echo cancellation system ( 11 ) of claim 17 , wherein the residual echo suppressor ( 14 ) operates in a frequency domain implemented as a Discrete Fourier Transform (DFT) domain and the second control signal ( 54 ) is determined in the frequency domain, implemented as the Discrete Fourier Transform (DFT) domain, as follows: W ( Ω , k ) = Φ E ( Ω , k ) - Φ B ( Ω , k ) Φ E ( Ω , k ) , wherein W(Ω,k) is a further transfer function signal provided to a residual echo suppressor ( 14 ) in the form of the DFT and, Φ E (Ω,k) and Φ B (Ω,k) are power spectral density (PSD) signals of the echo reduced microphone signal e(i) ( 34 ) and b(i)=d(i)−d′(i) is a residual echo signal equals to a difference between an echo signal d(i) and an estimate echo signal d′(i) ( 32 ) with frequency and frame indexes Ω and k, respectively; wherein the Φ B (Ω,k) is determined as Φ B (Ω, k )=β 1 ( k )Φ X (Ω, k ), where β 1 (k)=β 1 (i) is the coupling factor estimated at a time corresponding to the end of a frame.
21. A method for acoustic echo control, comprising the steps of: providing ( 60 ) an echo signal which is a component of a microphone signal ( 28 ) of a microphone ( 18 ) which is responsive to an echo signal ( 22 ) from a loudspeaker ( 16 ) that provides an acoustic output signal in response to a voice signal ( 20 ); and providing ( 76 ) a first control signal ( 46 ) to an echo canceller ( 10 ), a second control signal ( 54 ) to a residual echo suppressor ( 14 ) and a third control signal ( 48 ) to a residual echo filter ( 42 ) by a control block means ( 40 ) which is responsive to the speech signal ( 20 ), to an echo reduced microphone signal ( 34 ) and to a further echo reduced microphone signal ( 52 ) for optimizing cancellation of the echo signal.
22. The method of claim 21 , wherein the first control signal ( 46 ) is a transfer function signal provided to the echo canceller ( 10 ), said transfer function signal weights the voice signal ( 20 ).
23. The method of claim 21 , wherein the second control signal ( 54 ) is a further transfer function signal provided to the residual echo suppressor ( 14 ), said further transfer function signal weights an echo reduced microphone signal ( 34 ).
24. The method of claim 21 , wherein the third control signal ( 48 ) is a residual transfer function signal provided to the residual echo filter ( 42 ), said residual transfer function signal weights the voice signal ( 20 ).
25. The method of claim 21 , prior to the step of providing ( 108 ) the first, the second and the third control signals ( 46 , 54 , 48 ), further comprising the step of: determining ( 72 , 74 , 66 ) the first, the second and the third control signals ( 46 , 54 , 48 ) by a statistical adaptive-filter controller ( 40 ).
26. The method of claim 21 , further comprising the steps of: providing ( 82 ) an estimate echo signal ( 32 ) by the echo canceller ( 10 ) using the first control signal ( 46 ) provided by the controlled block means ( 40 ); and providing ( 84 ) the echo reduced microphone signal ( 34 ) by an adder ( 28 ) by adding the estimate echo signal ( 32 ) to the microphone signal ( 18 ).
27. The method of claim 26 , further comprising the steps of: providing ( 82 ) a further estimate echo signal ( 52 ) by the residual echo filter ( 42 ) using the third control signal ( 48 ) provided by the controlled block means ( 40 ); and providing ( 84 ) a further echo reduced microphone signal ( 52 ) by an adder ( 50 ) by adding a further estimate echo signal ( 50 ) to a microphone signal ( 18 ).
28. The method of claim 27 , further comprising the steps of: providing ( 86 ) an output system signal ( 36 ) by the residual echo suppressor ( 14 ) using the second control signal ( 54 ) provided by the control block means ( 40 ).
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
June 17, 2004
August 2, 2005
Browse 5M+ US patents with plain-English claim translations and AI-generated analysis.